Filter out NS non-key events from `where-is-internal'

Filter out NS non-key events from `where-is-internal'

* doc/lispref/keymaps.texi (Scanning Keymaps): Document it.
* lisp/keymap.el (make-non-key-event): New function.

* lisp/term/common-win.el (x-setup-function-keys): Mark ns events
as not being keys (bug#55940).

* src/keymap.c (Fwhere_is_internal): Filter out key sequences that
are marked as being non-keys.